Despite recent advances in assessment instruments for adolescents who abuse drugs and/or alcohol, the field of adolescent drug/alcohol assessment continues to be in need of further development. A new instrument which shows promise is the Comprehensive Addiction Severity Index for Adolescents (CASI-A), a multidimensional, adolescent-specific assessment tool for evaluating drug/alcohol use and psychological severity. The CASI-A is a semi-structured interview which obtains clinically-pertinent information designed to guide treatment planning, evaluate treatment outcome, and inform health policy. The CASI-A's design makes it suitable for administration in a variety of settings, for repeat administration at follow-up evaluations, and for assessment of all adolescents regardless of their admission profile. The CASI-A has evolved over the past 6 years to a point where it has encouraging evidence of reliability and validity. In order for the CASI-A to be incorporated into the clinical and research processes of adolescent treatment programs and in order for the information to be used to inform critical decision making at both the public health and individual level, additional inquiry into the CASI-A's psychometric properties among adolescents analyses, we believe that psychometric testing can be accomplished in a very cost efficient manner. Consequently, this grant application is being submitted to: (1) Empirically refine the CASI-A's scoring system; (2) Examine test-retest reliability; (3) Investigate concurrent validity of the Alcohol/Drug, Psychiatric, Education, and Legal Modules; (4) Investigate predictive validity; (5) Explore psychometric properties among four adolescent subgroups to ascertain for which adolescent populations the CASI-A will be an appropriate assessment tool. Four subgroups of 125 adolescents at each of four treatment sites will be entered into the four-year study over a 24 month period: (1) adolescents receiving residential treatment for drug and alcohol abuse; (2) adolescents receiving inpatient psychiatric treatment for primary psychiatric problems; (3) adolescents receiving both drug/alcohol and psychiatric treatment; (4) adolescents participating in court- stipulated detention. Male and female subjects will be a racially diverse group and will participate in two CASI-A interviews during treatment (primarily for reliability purposes) and a three- and six- month follow-up CASI-A interview (primarily for predictive validity purposes). Cronbach's alpha statistic, oblique, multiple-group, principal-components cluster analysis, multiple discriminant analysis, canonical variance analysis, intraclass correlation coefficients and pearson correlation coefficients will be the primary statistics used for examination of the CASI-A's psychometric properties.